From british royalty to reality tv stars if you open almost any entertainment magazine these days you are likely to see a picture of a celebrity looking stunningly fit weeks or months after giving birth. They almost make it seem, well, easy. But do these striking before/after transformations place undue and unfair pressure on other new moms? Here's abc's paula faris. Reporter: Kim kardashian tweeted the ultimate selfie this week designed to induce mom envy everywhere. The post baby body pic its a right of passage for celebrity whose want to tell the world they're back in business. Giselle, jessica alba, photos of gorgeous, fit new moms, a few months postpartum, seem to be the new norm. The fact is when you are surrounded by that imagery it affects how we feel about our body image. We can't meet it. And this week it may have been imagery overload. Here is princess kate looking impossibly thin three months after producing a royal heir. And new mom, kim kardashian, showing it all off post baby. Social media responded swiftly. You are a mom, don't forget, have some respect for being a mommy. As long as you are happy it is your life, not ours. Boom. But perhaps the biggest reaction was saved for a former miss bikini of california and mom of three, posting this photo boldly asking, what is your excuse? One tweet responding, no one likes a showoff. Four, three, two. She is making no apologies. I didn't call you fat? I didn't call you lazy? I didn't say you should look like me. I never said that new moms barely have time for a long shower or a hot bath. The idea of finding time to work out every day is nearly impossible. So, a lot of people are insulted by this. Go ahead, bring it down. Reporter: The working mom says she find time to exercise five or six days a week. Often with this group of sacramento moms as they told our reporter. I don't think she is trying to preach to anybody. More so trying to inspire women. Any one who is going to be mad is, is jealous and lazy. Bring it up, hold that. Reporter: The pressure to lose weight fast has sparked an industry targeting new mom whose want to look sexy pushing the stroller. Workout guru tracy anderson built an empire around keeping celebrity moms fit both during and after pregnancy. Really keeping our butt as lifted as we possibly can during the pregnancy. Reporter: She trains hollywood a listers even went into business with client and friend gwyneth paltrow. But for most moms, looking like paltrow is impossible. Don't you think you are partly responsible for creating the standard that we have to look a certain way. I hate that, actually. I really do believe that every single one of us is really beautiful and especially we're beautiful when we are working to connect to our body, when we are working to be our personal best. I think that's beautiful. Reporter: Is it fair to expect women who have recently had a baby to get into shape so quickly though? All awe first of all, everybody's life is unique. As soon as your doctor releases you to work out you have to start reconnecting to your body. What's hard is that you know what it is look to start working out again after being pregnant. It's the worst thing ever. Reporter: Among anderson's celebrity clients, none other than kim kardashian who was skewered in the tabloid for gaining weight during her recent pregnancy. I feel badly for her. Anybody who has to do that -- under the pressure of being photographed all of the time. You know, like sometimes when you are pregnant, the last thing you want to do, you want to be in sweats, you look like a house. Reporter: Anderson has clearly worked her magic. Its it good for the rest of us? I think women feel like they fall short. They feel like they haven't done it the right way or enough. And that's problematic. Reporter: Unlike most of us, celebrities have armies of people to help them get their post baby bod. I have patients in my practice who are celebrities who that is their work. They spend four to five hours in the gym every day, three to four times a week. That's what they do. At the same time I have every day women who have full time jobs, who are maybe have a baby at home. They have to rush home after work. They would much prefer to spend time with their children than at the gym. And they're going to take a little longer. Reporter: Meet alley carlin, a stay at home mom to two kids. Toddlers. It has been a challenge the last year and a half, losing my baby weight from my second kid. She swears by soul cycle, a workout for moms looking shoe shed baby weight. A large percentage of my client are moms. I would say upward of 80%. Reporter: An intense indoor cycling class where you can burn hundreds of calories in a single ride. I think there are so many people out there, like gisele, who have a baby, two weeks later in bikinis on the beach. I want to look good after having kids and be a good role model for my kids. Reporter: For "nightline," paula faris, in new york.

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